The present invention relates to plasma-processing apparatus and method for plasma-cleaning pads on a chip and pads on a board to which chips are mounted, and a plasma-processed board, and further relates to a chip mounting method employing the plasma-processing method and a chip mounted assembly.
A plasma-cleaning process, which is known, removes a dirt on a pad at the sides of a position for mounting a chip on a printed circuit board or on a pad on the upper surface of the chip prior to a wire bonding to the pad. In the plasma-cleaning process, the board including the chip mounted thereon is placed in a chamber of a plasma-processing apparatus, in which plasma is generated, and ions and neutral particles called radicals collide with the surface of the chip to remove the dirt on the board. After the plasma-cleaning process, the pad on the chip and the board are connected with wires by a wire bonding apparatus. Finally, the chip and the wires are covered with a resin by mold sealing.
FIG. 7 is a side view of a board including a conventional resin mold 6xe2x80x2. A chip 2 is mounted on a chip-mounting position 1xe2x80x2 of a board 1. A Pad 3 at the side of the position 1xe2x80x2 is connected to a pad 4 on the upper surface of the chip 2 with a wire. The resin mold 6xe2x80x2 is provided for protecting the chip 2 and the wire 5 by mold sealing.
As denoted by the solid line in FIG. 7, the resin mold 6xe2x80x2 flows wide and flattens around the chip 2 but is not domed. This causes the top of the wire 5 to be exposed out of the resin mold 6xe2x80x2. A desired shape of the resin mold 6 is denoted by the dotted line keeping a dome shape to encapsulate the chip and wire 5.
The reason why the resin mold 6xe2x80x2 is not domed but flattened is explained below. In a conventional plasma-processing apparatus, the board 1 has an entire surface exposed for plasma for the plasma-cleaning. As being plasma-cleaned, the entire surface has an increased wetting property. Accordingly, the resin used with resin mold 6xe2x80x2 has increased adhesive properties. And therefore, the molded form of the resin may thus flow extensively around the chip and flatten over the upper surface of the board 1 before being cured down. As a result, the resin mold 6xe2x80x2 has a flat shape as denoted by the solid line in FIG. 7.
A plasma-processing apparatus for plasma-cleaning a board having a chip and a pad-disposed area around the chip includes a chamber for accommodating the board, an electrode disposed at the chamber for generating plasma in the chamber by a high frequency voltage applied to the electrode; a table for supporting the board in the chamber, and a masking member provided above the board and having an opening for exposing the chip and the pad-disposed area to the plasma.
A plasma-processing method using the plasma-processing apparatus includes a process of applying a voltage to the electrode to generate plasma in the chamber; and a process of exposing the chip and the pad area to the plasma through the opening of the masking member for performing the plasma-process.